1. Field of the Invention
The present invention relates to a method of adding silicon to pure aluminum or an aluminum alloy.
2. Description of the Related Art
An aluminum-silicon alloy is widely used in various technical fields. In the initial stage of manufacture, the alloy was manufactured by the cast article manufacturers by adding required components to the pure aluminum. In the subsequent stage, the specialist alloy manufactures came to manufacture the aluminum-silicon alloy. However, marked improvements have been achieved recently in the melting equipment, and the analytical apparatus has come to be available at a low cost, with the result that the cast article manufacturers pay attentions again to the manufacture of the aluminum-silicon alloy.
The specific method of silicon addition widely accepted nowadays includes (A) elemental silicon addition, or (B) addition of aluminum-silicon mother alloy. In method A, however, the molten silicon has such a high temperature as 1414.degree. C. Naturally, it is difficult to maintain the molten silicon at such a high temperature over a long time, leading to an rendered unsatisfactory in the case where the surfaces of the silicon particles are heavily oxidized or where the oxidation reaction of silicon is promoted under the state of a high temperature. What should also be noted is the necessity of removing impurities. To be more specific, the alkali metal or the like contained in the reducing agent, which is used in the manufacture of silicon, forms a slug of silicates, and the unreacted fluorite remains in the manufactured silicon. Further, a very hard compound of silicon carbide is left in the manufactured silicon. Naturally, it is necessary to remove these impurities.
Method (B), i.e., addition of aluminum-silicon mother alloy. invites an increased material cost. Specifically, the aluminum-silicon mother alloy contains only 20 to 25% by weight of silicon. Thus, it is necessary to add a large amount of the mother alloy, leading to an increased material cost noted above. Further, the increase in the addition amount of the aluminum-silicon mother alloy causes the melt temperature to be lowered, leading to an increase in the melting cost.
Various metals other than silicon are known to be added to aluminum for forming aluminum alloys. In many cases, the additive metals have a specific gravity higher than that of aluminum and, thus, can be added to molten aluminum relatively easily. For example, the specific gravity of manganese is 7.2, which is about three times as high as 2.7 for aluminum. On the other hand, the specific gravity of silicon is only 2.4. Naturally, manganese can be added to molten aluminum very easily, compared with the silicon addition. In addition, manganese a melting point of 1245.degree. C. in contrast to 660.2.degree. C. for aluminum. Further, silicon has a melting point of 1414.degree. C., which is higher than . that of manganese. The high melting point of silicon is considered to make it difficult to add silicon to aluminum.